U.S. patent application number 16/604896 was filed with the patent office on 2020-05-21 for hydropower plant for controlling grid frequency and method of operating same.
The applicant listed for this patent is VOITH PATENT GMBH. Invention is credited to MARTIN BRUNS, THOMAS FOITZIK.
Application Number | 20200158076 16/604896 |
Document ID | / |
Family ID | 61868515 |
Filed Date | 2020-05-21 |
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United States Patent
Application |
20200158076 |
Kind Code |
A1 |
FOITZIK; THOMAS ; et
al. |
May 21, 2020 |
HYDROPOWER PLANT FOR CONTROLLING GRID FREQUENCY AND METHOD OF
OPERATING SAME
Abstract
A hydropower plant for regulating the frequency of an electric
grid has an upper water reservoir, a lower water reservoir, and a
waterway that connects the upper water reservoir to the lower water
reservoir. A turbine is arranged in the waterway and includes a
runner, a guide vane apparatus and a device for blowing out the
runner space. An electric double-fed asynchronous machine is
mechanically connected to the turbine and a frequency converter is
electrically connected to the asynchronous machine. A mains
transformer is electrically connected to the asynchronous machine,
frequency converter and mains grid. A resistor is arranged in a DC
intermediate circuit of the frequency converter in such a way that
it may connect the line sections of the DC intermediate circuit to
one another. There is also provided a device for cooling the
resistor.
Inventors: |
FOITZIK; THOMAS; (NEULER,
DE) ; BRUNS; MARTIN; (HEIDENHEIM, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOITH PATENT GMBH |
HEIDENHEIM |
|
DE |
|
|
Family ID: |
61868515 |
Appl. No.: |
16/604896 |
Filed: |
March 29, 2018 |
PCT Filed: |
March 29, 2018 |
PCT NO: |
PCT/EP2018/058121 |
371 Date: |
October 11, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03B 13/08 20130101;
H02J 3/48 20130101; H02J 2300/20 20200101; H02K 11/046 20130101;
F05B 2220/70646 20130101; H02P 9/02 20130101; H02K 7/1823 20130101;
H02J 3/381 20130101; H02J 3/28 20130101; H02J 3/46 20130101; F03B
13/06 20130101; Y02E 10/226 20130101 |
International
Class: |
F03B 13/08 20060101
F03B013/08; H02P 9/02 20060101 H02P009/02; H02K 11/04 20160101
H02K011/04; H02K 7/18 20060101 H02K007/18 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2017 |
DE |
10 2017 107 992.0 |
Aug 10, 2017 |
DE |
10 2017 118 194.6 |
Claims
1-12. (canceled)
13. A hydropower plant for regulating the frequency of an electric
grid, the hydropower plant comprising: an upper water reservoir and
a lower water reservoir, wherein a water level of the upper water
reservoir lies above a water level of the lower water reservoir; a
waterway connecting the upper water reservoir with the lower water
reservoir; a turbine arranged in the waterway, the turbine
including a runner, a guide vane apparatus and a device for blowing
out a runner space; an electric double-fed asynchronous machine
mechanically connected to the turbine, the double-fed asynchronous
machine including a rotor and a stator; a frequency converter
electrically connected to the rotor of the double-fed asynchronous
machine, the frequency converter having a DC intermediate circuit;
a mains transformer electrically connected to the frequency
converter, to the stator of the double-fed asynchronous machine and
to the mains grid; a resistor arranged in the DC intermediate
circuit of the frequency converter and configured to connect line
sections of the DC intermediate circuit to one another; and a
device for cooling the resistor.
14. The hydropower plant according to claim 13, further comprising
a pump for pumping water from the lower water reservoir into the
upper water reservoir, the pump having an independent drive.
15. The hydropower plant according to claim 14, wherein the pump
comprises a variable speed drive.
16. The hydropower plant according to claim 14, wherein the pump
comprises a drive with constant speed.
17. The hydropower plant according to claim 13, wherein the
frequency converter is a voltage source inverter (VSI).
18. A method of operating a hydropower plant, the method
comprising: providing a hydropower plant according to claim 13; in
a step V1, blowing out the runner of the turbine and operating the
double-fed asynchronous machine in phase-shifter mode; in a step
V2, receiving a request for the hydropower plant to provide fast
control power, thereby: if power output is requested: in a step
V31, braking the double-fed asynchronous machine with the frequency
converter; in a step V32, opening the guide vanes of the turbine
and starting controlled turbine operation; if power absorption is
requested: in a step V41, absorbing with the frequency converter
power from the mains grid and causing the resistor to convert
energy into heat.
19. The method according to claim 18, further comprising, if power
absorption is requested: in a step V42, starting the pump and
starting controlled pump operation.
20. The method according to claim 18, wherein step V41 comprises
accelerating the double-fed asynchronous machine with the frequency
converter.
21. The method according to claim 18, wherein step V31 comprises
braking the double-fed asynchronous machine to a minimum
permissible rotational speed.
22. The method according to claim 18, wherein step V41 comprises
accelerating the double-fed asynchronous machine to a maximum
permissible rotational speed.
23. The method according to claim 22, which comprises accelerating
the double-fed asynchronous machine with the frequency
converter.
24. The method according to claim 18, which comprises providing the
hydropower plant with a pump for pumping water from the lower water
reservoir into the upper water reservoir, the pump having an
independent, variable speed pump drive, and controlling the
controlled pump operation in step V42 with the variable speed pump
drive.
25. The method according to claim 18, which comprises providing the
hydropower plant with a pump for pumping water from the lower water
reservoir into the upper water reservoir, the pump having constant
speed drive, and wherein step V42 comprises opening the guide vane
apparatus of the turbine and controlling the controlled pump
operation by the frequency converter and the guide vane apparatus
of the turbine, wherein the turbine and the pump are in a hydraulic
short circuit.
Description
[0001] The present invention relates to a hydropower plant suitable
for rapidly controlling the grid frequency, and to a method for
operating such a hydropower plant.
[0002] Due to the inertia of the water column and the maximum and
minimum permissible water pressure in the waterways and turbine,
classical hydropower plants may only control electrical power
relatively slowly--typically on a timescale of 10-30 seconds. This
is not sufficient to contribute to short-term control of the grid
frequency in view of increased requirements. For example, the
National Grid Code of Great Britain requires that a certain
electrical power must be applied to the grid or absorbed in less
than a second, depending on the grid frequency, in order to
participate in the corresponding compensation. The object of the
present invention is to provide a hydropower plant that may provide
control power on a timescale of less than one second. Another
object of the present invention is to provide a method for
operating such a hydropower plant.
[0003] The inventors have recognized that the specified objective
may be accomplished by a hydropower plant with the features of
claim 1. Advantageous embodiments are set forth in the dependent
claims that depend from claim 1. The method according to the
invention for operating such a hydropower plant is set forth in the
independent method claim. Advantageous embodiments are set forth in
the dependent method claims
[0004] The solution according to the invention is explained below
with reference to the drawings. The drawings illustrate the
following, specifically:
[0005] FIG. 1 Hydropower plant according to the invention;
[0006] FIG. 2 Flow chart of the operation of a hydropower plant
according to the invention.
[0007] FIG. 1 shows the schematic structure of a hydropower plant
according to the invention. The hydropower plant comprises an upper
water reservoir marked 1 and a lower water reservoir marked 2, the
water surface of the upper water reservoir 1 being above the water
surface of the lower water reservoir 2. The reservoirs 1 and 2 may
also be natural waters, for example lakes or rivers. The hydropower
plant also comprises a waterway marked 3 that connects the upper
water reservoir 1 with the lower water reservoir 2. A turbine
marked 4 is arranged in the waterway 3. The waterway 3 is
consequently divided into two parts. The part above the turbine
4--the pressure pipe--is marked 31, and the part below the
turbine--the draft pipe--is marked 32. The turbine 4 has a turbine
runner, a guide vane apparatus and a device for blowing out the
space around the turbine runner so that when blown out the turbine
runner may rotate in air, with the closed guide vane apparatus
preventing the air from escaping toward the upper water reservoir.
The turbine may optionally be equipped with additional closing
members, for example a ball valve, in addition to the guide vane
apparatus. The turbine 4 is coupled to an double-fed asynchronous
machine marked 5. The double-fed asynchronous machine 5 comprises a
rotor and a stator. The rotor of the double-fed asynchronous
machine 5 is electrically connected to a frequency converter marked
6. The frequency converter 6 is connected to the mains grid via a
mains transformer marked 7. The stator of the double-fed
asynchronous machine is directly connected with the transformer
7.
[0008] There is a resistor in the DC intermediate circuit of the
frequency converter 6 that may be switched in such a way that it
connects the line sections of the DC intermediate circuit with each
other. The resistor is marked with 8. The hydropower plant also
optionally comprises at least one pump that is marked with 9 and is
arranged to pump water from the lower water reservoir 2 into the
upper water reservoir 1. The pump 9 may comprise its own closing
members and has its own independent drive with a mains
connection.
[0009] FIG. 2 shows a schematic flowchart method according to the
invention for operating a hydropower plant according to the
invention. In the step marked V1, the hydropower plant is in the
following state: The runner of the turbine 4 is blown out so that
it may rotate in air. The double-fed asynchronous machine 5 runs in
phase-shifter mode, i.e. the rotor thereof rotates according to the
grid frequency (i.e. within the permissible slip band) and,
depending on the excitation state, reactive power may be supplied
to the mains grid either capacitively or inductively. Due to the
coupling of the double-fed asynchronous machine 5 and the turbine
4, the runner of the turbine 4 rotates at the same rotational speed
as the rotor of the double-fed asynchronous machine 5. In the step
marked V2, a request is sent to the hydropower plant to actively
provide fast control power. The request may be to quickly deliver
power to the grid or to quickly receive power from the mains grid.
In the first case, the steps on the left branch of the flow chart
are followed; in the second case the steps on the right branch are
followed.
[0010] Power output to the mains grid: In the step marked V31, the
double-fed asynchronous machine 5 and connected turbine 4 are
braked via the frequency converter 6. The energy stored in the
angular momentum of the rotating components is output to the mains
grid. The procedures that take place in step V31 are very fast and
therefore the requested power may be delivered to the mains grid in
less than one second. In the step marked V32, the guide vane
apparatus is opened, together with other closing members of the
turbine 4 if applicable. This allows water to enter the previously
blown-out area around the runner of the turbine 4 from the upper
water 1. The air is expelled in the direction of the lower water
reservoir 2. The water flow accelerates the turbine 4 and the
double-fed asynchronous machine 5 back to a higher speed; thus,
power may be durably output to the mains grid. The procedures of
step V32 are initiated simultaneously with the procedures of step
V31. However, because the procedures of step V32 are much slower
than those of step V31, they only become effective much
later--usually after approximately 15-20 seconds. Before this, the
power output to the mains grid is determined by the procedures of
step V31. In step V31, the power output to the mains grid is
controlled by the frequency converter 6; in step V32, it is
controlled by the controller of the turbine 4 with the aid of the
guide vane apparatus.
[0011] Power absorption from the mains grid: In the step marked
V41, the frequency converter 6 draws power from the mains grid.
This power is converted into heat via the resistor 8. For this
purpose, the resistor 8 must be cooled. It is advantageous if part
of the power that the frequency converter 6 draws from the mains
grid is used to accelerate the double-fed asynchronous machine 5
and the runner of the turbine 4. Thus less energy needs to be
converted into heat in the resistor 8. The procedures in step V41
are very fast and therefore the required power may be absorbed from
the mains grid in less than one second. The procedures described in
step V41 may in principle be used by themselves to absorb power
from the mains grid over a longer period of time alone. However,
energy is constantly converted into heat and thus, as it were,
destroyed. It is accordingly advantageous if the energy is only
briefly converted into heat in V41. In the optional step marked
V42, the optional pump 9 is started up in order to pump water from
the lower water reservoir 2 to the upper water reservoir 1. As a
result, additional power is absorbed from the mains grid and the
energy that the pump 9 absorbs is converted into potential energy
of the water and stored for later use in turbine operation. The
procedures of step V42, in this case, are initiated simultaneously
with the procedures of step V41. Because the procedures of step V42
are much slower than those of step V41, however, these procedures
take longer to come to bear--usually after approximately 10 to 15
seconds. Before this, the power absorption from the mains grid is
determined by the procedures of step V41. In step V41, the
frequency converter 6 controls power absorption from the mains
grid. In step V42, power absorption from the mains grid may be
controlled in two ways: Either the pump 9 has a variable speed
drive that is able to control the power that the pump 9 absorbs, or
the pump 9 is designed as a constant speed pump. In the latter
case, the frequency converter 6 controls the power absorbed from
the mains grid. The guide vane apparatus of the turbine 4 is used
for speed control. The double-fed asynchronous machine 5 produces a
corresponding electrical power that is fed into the grid. The
result is a situation known as a hydraulic short circuit. The net
power that the mains grid absorbs is then calculated from the pump
power minus the power that the double-fed asynchronous machine 5
produces. Plainly, the power that the double-fed asynchronous
machine 5 generates must be less than the pump power. Because the
frequency converter 6 is able to control the turbine power and thus
the power that the double-fed asynchronous machine 5 generates, the
net power absorption from the mains grid may also be
controlled.
[0012] After processing the request made in step V2 to provide fast
control power, the hydropower plant is returned to the operating
state described in step V1. The hydropower plant is then once again
ready to respond to another request.
[0013] Practical experience in designing a hydropower plant
according to the invention has shown that it is advantageous if in
step V31 the double-fed asynchronous machine 5 is braked to the
minimum permissible speed. It is also advantageous if the
double-fed asynchronous machine 5 is accelerated to the maximum
permissible speed in step V41. The frequency converter 6 may be
designed as a "Voltage Source Inverter" (VSI). A VSI has the
advantage that it enables power factor control as well as control
in what is referred to as "Low Voltage Ride Through."
[0014] In order for the hydropower plant to be able to optimally
provide control power as the Grid Code requires, the plant must be
designed in such a way that the capacity for power output to the
grid corresponds to the capacity for power absorption from the
grid. This requirement must be met over both the short and the long
term. The design of the hydropower plant according to the invention
is sufficiently flexible that this requirement may be met by an
appropriate design of the components.
* * * * *